In recent years, with the increase of the amount of communication and information, interest has focused on radio communication technology using a high-frequency band which can transmit large amount of information at high speeds. Especially in 60 GHz band, because license is unnecessary to the band of 2.5 GHz per one transmitter, communication is possible at a speed of 1 Gbps and over by using the above-mentioned transmitter.
However, because directionality becomes strong for electromagnetic waves of a high-frequency band, it is not possible to have communication using diffracted electromagnetic waves. For this reason, when a shielding such as persons enter suddenly between a plurality of radio communication devices, there is a problem of losing communication. Then, if communication is lost, the radio communication device (radio receiver-transmitter) using the electromagnetic waves of such high-frequency band needs to control a radiation pattern of an antenna of the radio communication device, needs to search the strongest electromagnetic wave among electromagnetic waves reflected with the walls of buildings, the walls of housings, etc. and needs to communicate using a path which is a propagation channel of this electromagnetic wave.
As one method to control the radiation pattern of an electromagnetic wave outputted from a transmitter of a radio communication device, for example, by controlling a phase of a signal transmitted from each antenna element using an array antenna, there is a method to convert the radiation pattern. Here, an array antenna is an antenna having a plurality of antenna elements aligned and arranged in an array shape.
FIG. 1 is a figure showing a composition of a radio transmitter disclosed in non-patent document 1. Non-patent document 1 adds phase to a signal transmitted from an antenna. Therefore, non-patent document 1 is adding phase using a phase shifter consisted of a high-frequency band to a local signal outputted from a local oscillator. However, the phase shifter for a high-frequency band has a great loss, and in order to make up for the loss a new amplifier is needed, and a circuit size becomes large. On top of this, there will be a problem of the power consumption to increase. Consequently, without using a phase shifter for a high-frequency band having a great loss, a method to compose a phase shifter by a baseband signal band, and to add phase of a signal transmitted from an antenna to a baseband signal, is proposed (refer to FIG. 1 of the non-patent document 1).
In patent document 1, a method to add phase to a baseband signal by carrying out an operation by a digital signal processing as indicated by mathematical formula (1) is disclosed (refer to FIG. 1 of the document).
                              (                                                    Iout                                                                    Qout                                              )                =                              (                                                                                cos                    ⁢                                                                                  ⁢                    θ                                                                                                              -                      sin                                        ⁢                                                                                  ⁢                    θ                                                                                                                    sin                    ⁢                                                                                  ⁢                    θ                                                                                        cos                    ⁢                                                                                  ⁢                    θ                                                                        )                    =                      (                                                            Iin                                                                              Qin                                                      )                                              (        1        )            
In mathematical formula (1), I (In-phase) out and Q (Quadrature phase) out indicates a baseband signal of which phase θ is added. Iin and Qin indicate a baseband signal of before having phase added. Baseband signals Iout and Qout having a digital signal processed to, modulate a local signal by an orthogonal modulator, and the signal after the modulation is transmitted from an antenna.
Further, in patent document 2, a method to connect in parallel a plurality of phase shifters (fixed phase shifters) which the phase shift quantity is fixed, and to appropriately select such fixed phase shifters according to a desired phase, is disclosed (refer to FIG. 1 of the document).    Patent document 1: Japanese Patent Laid-Open No. H5-063427 (FIG. 1)    Patent document 2: Japanese Unexamined Patent Laid-Open No. H9-505716 (FIG. 7)    Non-patent document 1: Arun Natarajanm et. al., “A 77-GHz-Phased-Array Transceiver With On-Chip Antennas in Silicon: Transmitter and LO-Path Phase Shifting”, IEEE Journal of Solid-State Circuits, pp. 2807-2819, 2006.